Active implanted medical devices comprise, for example, cardiac pacemakers, defibrillators, neurological machines, pumps for dispensing medical substances, and cochlear implants (collectively hereinafter referred to as "implants"). Although the following description refers to active implanted medical devices, the present invention, is not limited to active implanted medical devices, but it applies as well to medical devices which are not implanted (for example, devices carried or worn by the patient) and medical devices which are not active (for example, those devices, whether or not implanted, that do not have a source of energy, and which use a portion of the energy of the interrogation signal that is applied to the device, for the emission of messages to the exterior. These devices, once put in place (principally by implantation), are programmed from the exterior by means of a remote or distant console which is commonly called a "programmer". The verification of parameters of the implant and/or the transmission of information recorded by the implant are typically realized by electromagnetic inductive coupling, called "telemetry"in the technique in question. The programmer is typically supplied with a receiver or head that is placed in face of, that is in proximity to the site of, the implant. This head comprises an antenna or coil that collects the magnetic field emitted from or generated by the implanted device by which data or information is communicated.
When one operates a transmission of information from the implant to the programmer, the nature of the material used in the construction of the housing of the implant (also known as the "case" as it will be hereinafter referred) should be taken into account. Indeed, the case is generally formed of a metallic material such as titanium. This material, due to its electrically conductive properties, has a current induced as a result of a transmission of data or information by telemetry, i.e., the main magnetic field or the useful signal. The induced current operates to re-emit a compensatory (parasitic) magnetic field that combines with, and has the effect of a low-pass filter on, the main magnetic field. This low-pass filtering introduces a distortion of a type known as "inter-symbol interference" or "inter-symbol jamming" or "longitudinal interference". It has, as an effect, in a given sequence of symbols (units of information), an overflow of one symbol on the following symbol. For adjacent symbols, this distortion becomes significant and can introduce ambiguities during the decoding of symbols.